The brinjal (Solanum melongena) is a warm-season crop grown for its edible fruit.
Climate is one of the most important factors that determine planting times, and the wide climate variation in SA means that good-quality brinjals can be grown in open lands across various parts of the country year-round.
The brinjal cannot tolerate very low temperatures; the minimum it can withstand is around 10°C, and the maximum is 34°C. The optimum temperature for brinjal cultivation is between 26°C and 29°C.
The earliest seedling establishment period is when soil and air temperatures meet the minimum requirements for plant growth. The latest seedling establishment period should allow for growth and harvesting to be completed before adverse conditions set in.
Generally, establishment periods for the main production areas are:
- Lowveld (frost-free areas): February to May;
- Middleveld (moderate areas): September to December;
- Highveld (cold areas): October to November;
- Western Cape: October to December.
Preferred soil types
Brinjals favour a well-drained loam to sandy loam soil, but will grow reasonably well in a wide range of different soil types.
However, certain criteria in terms of the soil structure and content must be met to make the crop commercially viable.
These include nutrient composition, compaction, effective soil depth, pH, crop rotation, herbicide residue and the water-holding capacity of the soil.
Different varieties produce fruit of different sizes, shapes and colours, varying from white to yellow or green, reddish-purple and dark purple.
The currently favoured cultivars produce a fruit that is egg-shaped, 12cm to 25cm long and 6cm to 9cm in diameter, and has a dark purple skin.
How to prepare the soil
Good soil preparation will improve the potential for profitable brinjal production. Primary soil preparation must create growing conditions that enable the plants to develop the optimal root system.
Most roots occur in the top 600mm of the soil.
Soil preparation depends on the soil type and the specific variety’s requirements. On sandy soils, the focus should be to reduce compaction and erosion; on heavier soils, the aim is to reduce crust formation.
Soil should be worked to a depth of between 200mm and 400mm.
Ridging is highly recommended, but this should be done according to the land contours.
This keeps excess water away from the plant, improves root zone aeration, increases soil depth in the growing bed and promotes root development.
Brinjals reproduce by seed. Seedlings should first be established in 128- or 200-hole trays and then transplanted. Although more expensive, the larger 200-hole trays ensure better root development.
Deep sowing is better in warmer conditions, as seedlings take longer to emerge at longer growing distances and cooler temperatures.
Shallow sowing is better under cooler conditions, as seedlings emerge sooner due to shorter growing distances and higher temperatures.
If possible, place seed at a uniform depth using a precision seeder. Grow the seedlings in a well-aerated medium, with good water-holding capacity and a pH of around 6,5. Peat, bark and vermiculite mixes provide good results.
Typical difficulties at this stage include an excessive tannin level and low soil porosity, resulting in poor drainage and green mould build-up. Pre-enrich the medium and fertilise the seedlings 10 days after germination, using a liquid fertiliser.
Keep the seedlings moist, but not wet, by using a watering can or hose with fine spray.
In summer, seedlings take four to six weeks to reach transplant maturity. In winter, they take approximately eight weeks.
Sources: ‘Eggplant Production Guideline’ (starkayres.co.za), Department of Agriculture.